Method and apparatus for improvements in convective heating

Abstract

The efficiency of a convective heating system employing an elongate firebox is dramatically increased by, inter alia, increasing combustion zone volume to approach that of the firebox and increasing residence time of rising combustibles at ignition temperatures.

I claim: 
     
       1. An improved convective heating system of the type having fireplace enclosure walls, a chimney with an apertured fireplace pan (74) for receipt of nascent products of combustion, and an elongate firebox (10) having bottom (12), top (14), back (16) and side walls (18) positioned in spaced relation to the corresponding fireplace enclosure walls and defining therewith a convective flow path of air across said firebox walls, said firebox having a front wall with a fuel receiving opening and a hearth area rearwardly of said front wall, the walls of the firebox defining an elongate volume of space within the firebox, the improvement comprising: (A) means, connected to the firebox, for maintaining an ignition temperature range substantially throughout that elongate volume of said firebox overlying said hearth area, said means including a flue assembly (20) having a flue extension (24) passing downwardly through the top wall of the firebox into the firebox with an opening (22) for receipt of nascent combustion products, the flue extension extending below the top wall of the firebox so as to create a blanket of hot combustion products (44) adjacent the firebox top wall, the flue assembly having a flue pipe (78) connected at one end to the outlet end of the flue extension and at its other end to the apertured fireplace pan (74) of the chimney for allowing the combustion products to pass up the chimney while preventing the convective flow path of air from passing up the chimney; and   (B) combustion air inlet means including a preheat manifold (28) mounted within the firebox and extending between the side walls of the firebox, the preheat manifold having at least one opening (50) at one end extending through the corresponding firebox side wall for receipt of combustion air and also having means for distributing this combustion air to the firebox hearth area.   
     
     
       2. The improved convective heating system of claim 1 wherein the opening at the end of the preheat manifold is positioned through the firebox side wall so as to bleed combustion air from the convected flow path of air defined between the firebox walls and the firebox enclosure walls. 
     
     
       3. The improved convective heating system of claim 1 including glass doors (54) for closing said fuel receiving opening; an elongate baffle (52) positioned in the firebox rearwardly of said doors and extending across the top of said fuel receiving opening; said elongate baffle extending downwardly to at least the level of the flue opening (22) for cooperating therewith to entrap the nascent combustion products above the flue opening in the air blanket (44). 
     
     
       4. The improved convective heating system of claim 3 wherein the preheat manifold has a rear wall and a top wall, the rear wall extending along the bottom wall of the firebox, the manifold separating the front wall of the firebox from the hearth area; and wherein the manifold means for distributing combustion air to the interior of the firebox hearth area comprises a plurality of inlet apertures spaced along the rear wall of said manifold, opening toward said hearth area; and wherein the lower distal portion of the elongate baffle extends rearwardly to overlie said preheat manifold. 
     
     
       5. The improved convective heating system of claim 4 wherein the means for maintaining an ignition temperature range throughout the firebox includes a baffle (26) positioned below the flue extension opening (22) for preventing direct entry of combustion products into the flue extension opening from burning fuel. 
     
     
       6. The improved convective heating system of claim 5 wherein the baffle is in the shape of a disc lying below the flue extension opening so that hot combustion products flow radially toward the flue assembly; and wherein the convective heating system further includes adjustable means depending from the flue extension and supporting the disc shaped baffle so as to adjust the distance between this baffle and the flue extension opening and thereby regulate the amount of combustion products that can flow into the flue extension opening. 
     
     
       7. The improved convective heating system of claim 4, further comprising a freestanding unit (84) and a fireplace enclosure (114) for receipt of the firebox (10), the fireplace enclosure having means for being spaced from the freestanding unit and thereby establishing a secondary convective flow path of air exteriorly of, and in heat exchange relation with, said first named convective flow path of air. 
     
     
       8. The improved convective heating system of claim 7 including an exterior exhaust flue (130) connected to the chimney and flue means extending between the flue assembly in said firebox and the exterior exhaust flue (130); and said flue means traversing in heat exchange relationship said secondary convective flow path of air. 
     
     
       9. The improved convective heating system of claim 8 wherein the portion of said flue means traversing said secondary flow path of air includes a flue trap; said flue trap comprising an offset inlet (126) connected to the flue assembly (20) for receipt of combustion products, an outlet 128 connected to the exhaust flue (130) for removal of combustion products, and a heat exchange member connected between the inlet and outlet and having a large surface area in comparison to an equal length of the remainder of said flue means. 
     
     
       10. An improved elongate firebox of the type having a central flue opening, a bottom, top, back and side walls, a frontal fuel receiving opening, and an elongate fuel support area of length "2 b" that exceeds the height "a" from said fuel support area to the top wall of said firebox as measured along the axis of said flue opening, the improvement comprising: (A) means, connected to the firebox for increasing the path length to the flue opening that products of combustion emanating from fuel located at ends of the fuel support area must travel from a value approaching √a 2  +b 2  to a value approaching a+b; said means including a flue assembly having an annular entry opening spaced below said top wall for momentarily entrapping rising products of combustion above the level of the annular entry opening;   (B) glass doors forming the fuel receiving opening in the firebox;   (C) a preheat manifold extending along the bottom wall of said firebox between the front wall thereof and the fuel support area and including a plurality of combustion air inlet apertures extending to and between remote ends of the firebox and at least one opening at one end of the manifold extending through the corresponding firebox side wall for receipt of combustion air;   (D) an elongate baffle positioned rearwardly with respect to the fuel receiving opening and extending downwardly below the length of the annular entry opening and rearwardly to overlie said preheat manifold; and   (E) common means in said central flue opening for selectively controlling central draft and combustion air admission.   
     
     
       11. An improved elongate firebox as defined in claim 10 wherein the means for increasing the path lengths to the flue opening that products of combustion must travel further comprises a second baffle positioned below the annular entry opening of the flue assembly for preventing direct entry of combustion products into the entry opening from the burning fuel. 
     
     
       12. An improved elongate firebox as defined in claim 11 wherein the baffle is in the shape of a disc having a diameter approximately equal to that of the annular entry opening and wherein the firebox further comprises adjustable means depending from the flue assembly and supporting the second baffle so as to allow adjustment of the distance between the second baffle and the entry opening and thereby regulate the amount of combustion products that can flow into the entry opening. 
     
     
       13. An improved firebox as defined in claim 12 wherein the annular entry opening of the flue assembly is spaced below the top wall of the firebox approximately 12% of the height from the top wall to the bottom wall of the firebox and the baffle is spaced below the opening of the flue assembly between approximately 50% and 100% the distance that the opening is spaced below the firebox top wall. 
     
     
       14. An improved convective heating unit as defined in claims 1, 2, 3, 6, 9, or 10 wherein the flue extension depends below the top wall of the firebox approximately 12% of the height from the top wall to the bottom wall of the firebox. 
     
     
       15. An improved elongate firebox of the type having a central flue opening, a bottom, top, back and side walls, a frontal fuel receiving opening, and an elongate fuel support area whose length "2 b" exceeds the height "a" from said fuel support area to the top wall of said firebox, the improvement comprising means, connected to the firebox for increasing the path length to the flue opening that products of combustion emanating from a discrete portion of said fuel support area horizontally spaced a distance "X", from the axis of said flue opening must travel, from a value approaching √a 2  +x 2 , to a value approaching; a+x, said means including a flue assembly having an annular entry opening spaced below said top wall, a disc shaped baffle having a diameter approximately equal to the diameter of the annular entry opening, the baffle spaced below the entry opening so as to allow the products of combustion to enter the entry opening throughout approximately 360 degrees, and means, connected to the flue assembly and the baffle, for adjustably positioning the baffle below the entry opening, where the distance "x" is equal to or less than "b". 
     
     
       16. An improved firebox as defined in claim 15 further comprising a preheat manifold extending along the bottom wall of the firebox between the side walls of the firebox and having open ends extending through the side walls of the firebox for receipt of combustion air, the manifold having a rear wall and a top wall defining a channel with the bottom wall of the firebox, the rear wall of the manifold including a plurality of combustion air inlet apertures extending across the entire length of the manifold for delivery of combustion air to fuel placed within the firebox for combustion. 
     
     
       17. An improved firebox as defined in claim 16, further comprising an elongated baffle positioned between the side walls of the firebox and extending rearwardly and downwardly from the front top of the firebox fuel access opening so as to substantially overlie the preheat manifold. 
     
     
       18. A free-standing convective heating unit for use with a chimney, comprising: (A) a free-standing unit (84) having bottom, back, side, and top insulative walls for defining a frontally open space, the top wall having an aperture communicable with a chimney for the escape of combustion products and at least one delivery conduit (86 or 88) for providing secondary convective air flow to a room;   (B) a fireplace enclosure (114) mounted within the frontally open space of the free-standing unit, having a bottom wall (106) spaced above the bottom wall of the free-standing unit so as to provide for secondary convective air flow therebetween, side walls (108), a back wall (110), and a top pan (112) having an aperture for passing products of combustion therethrough, the bottom wall, side walls, back wall and top pan defining a frontally open enclosure, and the back wall of the fireplace enclosure spaced away from the back wall of the free-standing unit so as to provide for a space between these walls for the secondary convective air flow, this space having access of air through portions of the fireplace enclosure and also communicating with the delivery conduit in the free-standing unit for removal of this secondary convective air flow to a room; and   (C) a firebox (10) mountable within the fireplace enclosure, having a bottom wall (12), top wall (14), back wall (16) and side walls (18) and pivotal glass doors at its front for defining a fuel access opening to the interior of the firebox, the firebox having legs (104) depending from the bottom wall of the firebox for spacing the bottom wall of the firebox above the bottom wall of the fireplace enclosure so as to define therebetween a space for the in-flow of primary convective air (96), the back wall of the firebox spaced from the back wall of the fireplace enclosure so as to define a space therebetween for the passage of primary convective air flow, and the top wall of the firebox spaced beneath the top pan of the fireplace enclosure so as to define a space therebetween for the exiting of the primary convective air flow (100) into a room, the firebox having a flue assembly passing through the top wall of the firebox to communicate with the aperture in the top wall of the free-standing unit for the escape of combustion products from the firebox, the firebox further having means communicating with the primary convective air flow for bleeding combustion air from this primary convective air flow into the interior of the firebox for combustion purposes; whereby the secondary convective air flow is in surrounding relationship with the primary convective air flow for the dual purpose of maintaining the walls of the free-standing unit at a relatively low temperature so that the unit may be enclosed within a room, and for purpose of obtaining secondary heat recovery between the fireplace enclosure walls and the free-standing unit for delivering this secondary convective air flow into a room for heating purposes, and wherein the primary convective air flow is delivered to the room for heating purposes with the combustion air obtained from the primary convective air flow and with the secondary convective air also obtained from the primary convective air flow.     
     
     
       19. The free-standing unit of claim 18 wherein the firebox means for communicating with the primary convective air flow comprises a preheat manifold on the bottom wall of said firebox extending across the full length of said fuel access opening, the manifold having a rear wall with a plurality of combustion air inlet apertures opening therefrom and extending along the full length thereof, the preheat manifold having opposed open ends extending through the corresponding firebox side walls for bleeding combustion air from the primary convective air flow. 
     
     
       20. The free-standing unit of claim 19 wherein portions of the fireplace enclosure that provide access of air for the secondary convective air flow comprise portal openings in the bottom, back and side walls of said fireplace enclosure. 
     
     
       21. The free standing unit of claim 20 including secondary heat exchange means in said secondary convective air flow, comprising: (1) flue extension means extending upwardly from said firebox, through the top pan of said fireplace enclosure and into an upper plenum defined between the top pan of said fireplace enclosure and the top wall of the free-standing unit; and   (2) a flue trap in said upper plenum comprising an offset inlet connected to the flue assembly for the receipt of combustion products, an outlet connected to the aperture in the top wall of the free-standing unit, and a heat exchange member connected between the inlet and outlet, and having a cross section and aggregate surface area which is large in comparison with the inlet and outlet cross-sectional areas, whereby hot flue gases are momentarily entrapped for secondary heat exchange with said secondary convective air flow.   
     
     
       22. the free-standing unit of claim 21 including a flue damper in the outlet of the flue trap; and the flue path from said firebox to said flue damper in the outlet of the flue trap being substantially fully open whereby combustion and firebox draft are controlled by the flue trap damper. 
     
     
       23. The free standing unit of claim 19 including a central flue in said firebox having an entry opening spaced below the top wall of said firebox and a baffle spaced below the entry opening for momentarily entrapping the hottest rising products of combustion thereabove before exiting into the entry opening. 
     
     
       24. A free-standing convective heating unit as defined in claim 18 or 19, wherein the flue assembly of the firebox has a flue extension passing through the top wall of the firebox with an opening for receipt of combustion products, the flue extension extending below the top wall of the firebox so as to create a blanket of hot combustion products adjacent the firebox top wall so as to maintain an ignition temperature range substantially throughout the entire volume of the firebox. 
     
     
       25. A free-standing convective heating unit as defined in claim 24, further comprising an elongated baffle positioned between the side walls of the firebox and extending rearwardly and downwardly from the front top of the firebox fuel access opening so as to substantially overlie the preheat manifold. 
     
     
       26. A method of effecting substantially complete combustion within an elongate firebox having bottom, top, back, and side walls, and having a central flue opening therein, an elongate fuel support area having a length "2b" that exceeds the height "a" from the fuel support area to the top wall of the firebox, comprising the steps of: (A) increasing the path length to the flue that products of combustion emanating from fuel located at ends of the fuel support area must travel from a value approaching √a 2  +b 2  to a value approaching a+b; by establishing a flow path of said products of combustion first upwardly above the level of said flue opening, then laterally toward said flue opening and then downwardly to exit said flue opening; and   (B) establishing a stoichiometric oxygen supply across the fuel support area.   
     
     
       27. The method of claim 26 including the step of preheating said oxygen supply. 
     
     
       28. The method of claim 27 including the step of establishing a primary convective air flow across the bottom, top, back and side walls of said firebox. 
     
     
       29. The method of claim 28 including the step of bleeding said oxygen supply from said primary convective air flow.